A Walmart ad in my local newspaper trumpets “75% of all Americans don’t get enough Vitamin D” and offers to sell me Maximum Strength Vitamin D3, 5000 IU capsules to “promote bone, colon and breast health.” Meanwhile, the Institute of Medicine (IOM) tells me that “the majority of Americans and Canadians are receiving adequate amounts of … vitamin D” and that no one should take more than 4000 IU a day. Apparently Walmart and the IOM aren’t talking to each other.

The media have been giving the impression that vitamin D is a new wonder drug. They have told us that we aren’t getting enough sunlight, that a large percentage of us suffer from vitamin D deficiency, and that low levels of vitamin D are associated with cancer, multiple sclerosis, peripheral vascular disease, diabetes, rheumatoid arthritis, Parkinson’s and Alzheimer’s disease, and other conditions. Low levels of vitamin D have been linked to higher overall mortality (but so have high levels of vitamin D!). The anti-vaccine folks have been telling us (without any controlled studies) that vitamin D supplements are better than vaccines for preventing influenza. There’s no good evidence that raising vitamin D levels with supplements actually prevents any of these conditions, but many people think it should, and doctors have increasingly been measuring blood levels and prescribing high dose supplements. Is this just another passing fad like the enthusiasm for vitamin C, or are we belatedly recognizing a serious deficiency problem?

I’ve had a lot of inquiries about “is this information trustworthy?” and “how much vitamin D should I be taking?” I’ve been telling people that I didn’t know, that recent findings will soon result in new recommendations, and I’ve been eagerly awaiting the new guidelines. Now we have them, thanks to the IOM. They are not what most of us anticipated. Since so many doctors had been advocating higher levels to prevent things like cancer, I thought official recommended intake levels would go up; instead, they went down.